Zinc(II) Iodide-Directed β-Mannosylation: Reaction Selectivity, Mode, and Application.

A direct, efficient, and versatile glycosylation methodology promises the systematic synthesis of oligosaccharides and glycoconjugates in a streamlined fashion like the synthesis of medium to long-chain nucleotides and peptides. The development of a generally applicable approach for the construction of 1,2--glycosidic bond with controlled stereoselectivity remains a major challenge, especially for the synthesis of β-mannosides. Here, we report a direct mannosylation strategy mediated by ZnI, a mild Lewis acid, for the highly stereoselective construction of 1,2--β linkages employing easily accessible 4,6--tethered mannosyl trichloroacetimidate donors.

ZnI-Directed Stereocontrolled α-Glucosylation.

Here we report a glucosylation strategy mediated by ZnI, a cheap and mild Lewis acid, for the highly stereoselective construction of 1,2---glycosidic linkages using easily accessible and common 4,6--tethered glucosyl donors. The versatility and effectiveness of the α-glucosylation strategy were demonstrated successfully with various acceptors, including complex alcohols. This approach demonstrates the feasibility of the modular synthesis of various α-glucans with both linear and branched backbone structures.